Ignition apparatus and method

ABSTRACT

The voltage across the spark gap is increased or amplified to ignite the gap when required, thus enabling ignition of the spark gap when required. The incremental voltage to obtain gap ignition is additive to any voltage already across the gap, and is additive irrespective of polarity. That is, if a possible overvoltage pulse arrives, the main gap has an increased positive voltage. If a negative overvoltage pulse arrives, the main gap has an increased negative voltage applied.

FIELD

The present application relates to the technology of igniting sparkgaps, particularly lightning type arrestors. The application alsorelates to lightning protection and transient protection.

One invention relates particularly to an apparatus and method adapted toignite the spark gap when line overvoltage is detected. Anotherinvention relates to alleviating excess line voltage caused bytransients or the passage of relatively high currents.

The present invention has application in many industries, particularlybut not exclusively electrical transmission lines andtelecommunications.

BACKGROUND

Spark gap type lightning arrestors have been used in order to protectelectrical equipment. In operation they conduct excess line voltagedelivered by lightning strikes to ground. The arrestors, by virtue oftheir configuration, have a spark gap which provided by an air gapdimensioned to not break down at system working voltages (linevoltages), but to breakdown by arcing at an overvoltage well in excessof line voltage, such as an overvoltage consequential upon a lightningstrike. The arc formed conducts the transient current, inherent in anovervoltage condition, to ground.

In order to ensure that the arc formed upon a lightning strike willextinguish after the overvoltage has been conducted to ground, the sparkgap is dimensioned relatively wide. As a consequence, it typicallyrequires approximately 3 kV to 4 kV across the gap to initiate thebreakdown arc on a 220-240 V, 50 Hz system.

Thus, before the breakdown arc is initiated, a situation can arise wherea line voltage of up to 4 kV is transmitted to equipment which issensitive to such excess voltage. This problem has to date been leftunaddressed.

Other arrestors incorporate a third electrode proximate one of the mainelectrodes. When activated, the third electrode creates a spark betweenit and one of the main electrodes. This spark forces the main gapbetween the main electrodes to avalanche. The problem in reducing thegap width is power follow-on current and formation of metal fingers fromgasified metal. These can short circuit the gap. Also, the enormoustemperatures (typically 5000°-8000° C.) and pressures in the triggeredarc cause severe burning of the trigger electrode (with virtuallywhatever material is used). Further, these type of arrestors arespecially constructed, relatively expensive, or have internal gaspressure reduced to control spark overvoltage.

Yet a further type of arrestor is the gas arrestor which has a spark gapencapsulated in a gas environment, the gas environment providing arelatively selected strike voltage. The gases typically used are neon,with a strike voltage of approximately 75V to 90V, and argon, with astrike voltage of approximately 230V. However, for example in thetelecommunications industry there is a need for over voltage protectionwith a strike voltage of approximately 60V, and to date this need hasalso been unaddressed.

Other problems related to prior art devices is that where the arrestoris configured to a set trigger voltage, it has been found that afterseveral operations, the trigger electrode can burn or deteriorate tosuch an extent that the original characteristics of break down voltageare partially or totally lost.

SUMMARY OF INVENTION

It is an object of the present invention to alleviate the problem of lowvoltage triggering of a spark gap type arrestor.

The present invention overcomes problems associated with the prior artby increasing the voltage across the spark gap.

This invention provides, in one form, an apparatus and method ofinitiating the firing of a spark gap, including:

a voltage means responsive to a trigger means, whereupon beingtriggered, the voltage means provides an additive voltage to the sparkgap.

The present invention is predicated on the concept of increasing oramplifying the voltage across the spark gap in order to ignite the gapwhen required thus enabling ignition of the spark gap when required. Theincremental voltage to obtain gap ignition is additive to any voltagealready across the gap, and is additive irrespective of polarity. Thatis if a positive overvoltage pulse arrives, the main gap has anincreased positive voltage. If a negative over-voltage pulse arrives,the main gap has an increased negative voltage applied.

In another form, there is provided an apparatus and method of triggeringthe firing of at least a two electrode spark gap device, including:

a voltage amplifier means adapted to increment or boost a trigger signalfor application to and to fire the spark gap.

The principle of utilizing a means of amplifying the trigger voltage inorder to ignite the spark gap can also be adopted in the presentinvention.

The voltage means is preferably embodied as a step-up transformer, butmay also be provided in the form of a voltage source. In one form, thetransformer is provided in series with the spark gap, the transformerhaving a toroidal winding.

The trigger means is preferably voltage sensitive in detecting anovervoltage line condition, and preferably can be set to trigger at anyvoltage level considered to be an overvoltage condition dependent on theapplication of the present invention. In one form, an avalanche deviceis used to pulse the voltage means.

The present apparatus and method is applicable to relatively lowvoltages and equally applicable to relatively high voltages. In thisregard, the disclosure of the present invention with reference to aspark gap arrestor with a spark gap ignition voltage of 3 kV to 4 kV isonly exemplary. The present invention can be implemented at triggervoltages well below 3 kV or well above 3 kV, dependent on the circuitand line conditions to which the present invention is applied. Forexample, if a 500V pulse arrives on the line, the present invention mayadd another 3 kV in series with the spark gap and cause the spark gap totrigger without the need for a third or other electrodes. In thisexample, 500V would be considered a line overvoltage and the presentinvention enables 3 kV plus 500V to be applied across the spark gap,causing the spark gap to fire at the line voltage of 500V, rather than 3kV.

The present invention is also applicable to the firing of a standardspark gap at atmospheric pressure.

The invention disclosed seeks to artificially reduce the natural sparkovervoltage by applying amplified, boosted and/or incremental voltagesto the spark gap.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram representing a basic principle utilized inaccordance with the present invention;

FIG. 2 is a diagram representing a first embodiment of the presentinvention;

FIG. 3 is a diagram representing another embodiment of the invention;

FIG. 4 illustrates an alternative embodiment to that of FIG. 3;

FIG. 5 represents still another embodiment of the invention;

FIG. 6 illustrates yet another embodiment of the invention; and

FIG. 7 illustrates a further embodiment of the invention.

Preferred embodiments of the present inventions will now be disclosed.

FIG. 1 illustrates the basic principle utilised in the presentinvention. An arrestor is provided between line and ground rails inorder to conduct overvoltage, i.e. excess voltage above the normal linevoltage, to ground. By passing current to ground as a result of thearrestors operation, voltage sensitive equipment can be betterprotected.

A trigger mechanism external to the arrestor and incorporating thevoltage means of the present invention can initiate the firing of thespark gap when an overvoltage condition is registered on the line.

The present invention can have one or more spark gaps to carry the fullcurrent. One gap is preferred, dependent on application. In respect ofthe triggering mechanism, it does not have to be a spark gap but it maybe a second (tiggering) gap which is only for the pulse into the triggertransformer. It would therefore only carry a relatively small current.The triggering mechanism could otherwise be a sidactor or other solidstate avalanche device. A gas arrestor is also another option.

For example, if the natural breakdown of the spark gap is 3000 volts, atrigger mechanism can be designed, for example to fire the spark gapwhen there is an applied pulse of 200 volts. A step up in thissituation, a step up voltage of 15:1 transformer or other mechanism canbe used to provide a voltage of 3000 volts across the spark gap. This3000 volts in conjunction in series with the 200 volt line voltageapplied would make a total of 3,200 volts. The spark gap would then firehaving this voltage applied across it.

One embodiment of the present invention is illustrated in FIG. 2. Theline voltage appears across C1 and C2. G1 is a voltage sensitive triggeror any type of voltage sensitive switch device. In the form illustrated,G1 is a gas arrestor, but may be a triac or any other type of suitableavalanche device. The voltage provided at the junction of C1 and C2,when high enough as in an overvoltage condition, is used to cause thetrigger G1 to fire. It can thus be seen that the values of C1 and C2together with the characteristic of G1 can be selected appropriately topredetermine or selectively determine the line voltage considered to beovervoltage, and at which the spark gap is to fire. When the trigger G1fires, the energy stored in C2 is dumped into T1.

T1 and T2 are an embodiment of the voltage means of the presentinvention. In this embodiment they are provided as a step-uptransformer, although any form of voltage amplifier can be used, such astransistors or op-amps. It is the function of the voltage amplifier toincrease or multiply the voltage provided by the trigger or line to alevel sufficient to ignite the spark gap.

In the embodiment illustrated the spark gap ignition voltage is of theorder of 3 to 4 kV. The amplifier means is thus configured to providethis voltage level as an ignition voltage to the spark gap when anovervoltage condition is registered.

If, for example, a line voltage of 400V or more is considered anovervoltage condition, a transformer ratio of 10:1 can be selected,together with appropriately rated trigger componentry to provide thenecessary 4 kV spark gap ignition voltage. If, for example, thetransformer winding ratio was 5:1, then again with appropriatecomponentry selected, a line voltage of 800V or more could then beconsidered an overvoltage condition.

The voltage appearing across T1, resultant from C2, is amplified inaccordance with the transformer winding ratio and is delivered to thespark gap.

L2 is used as a choke to prevent the ignition voltage from beingtransmitted directly to the line. When the arrestor fires, however, L2saturates to facilitate the flow of power from the line to ground.

C3 is used as a decoupling capacitor for the line 50 Hz.

L1 may be provided in isolation as a choke, or in conjunction with acapacitor to form an LC filter.

The spark gap arrestor may be a horn type or surface discharge type.

Another aspect of the present invention is that one or more componentscan be selected to set the level considered to be an overvoltagecondition. The amplifier means, the voltage sensitive trigger and/or thecapacitive ratios may be selected or designed to determine the flashovervoltage considered an overvoltage.

FIG. 3 illustrates another embodiment of the present invention. Thecircuit illustrated works similar to that of FIG. 2, however in theembodiment of FIG. 2, the line voltage almost totally appeared acrossthe spark gap and series inductors such as L2 were used to substantiallyprevent the ignition pulse back feeding to the line or power grid.

In FIG. 3, the amplifiers means is now coupled in series with thearrestor. To this end, the secondary winding T2 is coupled in serieswith the spark gap and between the line and ground rails. T2 is alsopolarized to add to the line transient voltage. In the embodimentillustrated, there is substantially no loading on the transformer untilthe spark gap fires. After firing, the core material of T2 will saturateand this will serves to reduce the series inductance observed by theimpulse current.

FIG. 4 illustrates an alternate to FIG. 3, and which operates in asimilar fashion to the circuit of FIG. 3.

In the embodiments disclosed in FIGS. 3, 4 and 5, the transformersecondary winding is in series with the main gap. The transformersecondary may be the actual trigger device, as it adds to the normalvoltage to force spark over. Thus the transformer secondary can add tothe applied line voltage to achieve gap firing.

In the embodiments illustrated is a unique way of triggering by addingvoltage in series with the spark gap. This is resultant from thetransformer being formed in a toroidal form, which when saturatedproduces a relatively low inductance. This factor is consideredimportant in these embodiments since the main discharge current flowsthrough these windings. Too much inductance, and the total residualvoltage increases. Normal transformers have windings laying along sideeach other causing an enhanced magnetic field, even if the coresaturates. If the north/south magnetic poles if each turn of a toroidalwinding are considered, the north/south line rotates. Thus, if ten turnsare used, the core field of each turn is 36° different in alignment tothat of its neighbor. In this way, the residual inductance is reducedwhen the core is saturated. Minimising this residual inductance is animportant aspect of using this type of embodiment.

This is due to the very high dl/dt of the lightning wavefront. Since thetrigger transformer is in series with the gap and carries full dischargecurrent, the voltage due to L dl/dt causes an increase in voltagereaching protected equipment. Values exceeding 5 μH would be consideredexcessive. Values of 1-1.5 μH can be achieved by the present invention.

FIGS. 5 and 6 relate to the situation of a relatively high dl/dt in thecircuit arrangement disclosed above.

The current passing through Ar1 and winding T2 may cause an increasedvoltage across line and ground rails. This has been found to occur dueto the inductance of the winding T2, even when the core of the step-uptransformer is saturated. For example, if the winding T2 in a saturatedcondition exhibits 4 μH, and dl/dt=1 kA/μsec, then V=L. (dl/dt)=4 kV.

It has been found that by providing a number of spark gap elements incircuit, each element being rated to conduct at a predetermined orselected voltage, the voltage caused by the relatively high dl/dt can beconstrained to within allowable levels. In this way, one gap element mayoperate over a relatively low voltage window, and if the line voltageincreases beyond that window, another gap element may operate over thenext window, and so on. For example, Ar1 may be a smaller gap and mayoperate at 0.5 to 4 kV, and Ar2 may be a larger gap and may operate atvoltages above 4 kV. Thus, in operation, element Ar1 will fire at arelatively low voltage given its relatively small gap, and element Ar2can fire at a relatively high voltage given that it has a gap relativelylarger than that of element Ar1. Element Ar2, when it fires, has beenfound to produce a limit on or modify the extent to which the linevoltage extends into an overvoltage condition. A tertiary protector inthe form of a metal oxide varistor may be provided downstream to furtherlimit the residual voltage.

In the circuit arrangement as illustrated in FIG. 6, the residualvoltage reaching the filter only exists for a few microseconds, and assuch is relatively easy to filter out. The resultant voltage reachingthe equipment to be protected may only be up to 20V or so above nominalline voltage. In this case, no tertiary protector is required.

Because of the use of the voltage amplifier of the present invention,and the many circuit parameters that can be chosen, the arrestor can becaused to fire over a range of voltages. This equally applies to theinventive aspect of providing a plurality of spark gap elements incircuit. The arrangements disclosed above have also been found to limittemporary overvoltages of the line, not just those resultant from alightning strike, but where the line voltage nevertheless increases toand beyond a voltage level determined to be considered an overvoltage.For example, a temporary overvoltage on a power grid may increase theline voltage up to 3-4 times the rated voltage for up to 5 seconds. Thistype of line condition can also be dealt with by the present inventions,individually or in combination.

Spark gap arrestors can create "co-ordination" problems with otherarrestors. For example, a spark gap may fire at 3.5 kV but an equipmentsupplier may have a 275 VRMS metal oxide varistor in his product. Thisvaristor, by means of a low clamping voltage, may prevent operation ofthe spark gap. Consequently, the lightning energy is wholly transmittedto the equipment. In the present invention it is possible to modify thespark overvoltage and eliminate co-ordination problems.

An adaptation of the present invention or "incremental voltagetriggering concept" is illustrated in FIG. 7 in its application totelecom lines. Using the circuit of FIG. 6, pulses of any polarity mayarrive on one or both lines.

The bridge makes all pulses unipolar as they apply to the avalancheswitch. In a preferred form, this will trigger at 70V and pass a pulsecurrent through T1 primary. The secondary of T1 is in series with theearth of a three element gas arrestor. It is polarised to add to theline voltage.

Normally, gas arrestors are rated 230V as ring voltages and battery canraise working line voltages to around 190V. But, on sensitive circuits,such as PABX line cards, this is too much. This circuit will allow 200Vto pass but force the arrestor to fire on fast transients. The R/Ccomponents around the avalanche switch preclude operation on lowfrequencies up to 200V. The T1 secondary uses core saturation to beeffective.

The reason for using gas arrestors is that they can bypass high energylevels. However, the drawback with using existing gas arrestors is thatthey are preset to trigger at voltages such as 75, 90 or 230 volts ormore. These said voltages are thus considered unsuitable for manyapplications, for example where a circuit must be designed to arreststrike voltage above 60 volts. The present invention, advantageously,can add 30 volts to an existing 60 volt line voltage in order to triggera 90 volt gas arrestor or, on the other hand, can add 170 volts to anexisting 60 volt line voltage to trigger a 230 volt gas arrestor. Thecircuit of the present invention, that is the voltage amplifiermechanism can suitably be configured depending on the application.

I claim:
 1. An apparatus adapted to initiate the firing of a spark gapin response to a transient or overvoltage condition, the apparatusincluding voltage means for applying an additive voltage to the sparkgap, the additive voltage being applied in electrical series with a linevoltage across the spark gap to provide a total voltage across the sparkwhich exceeds the line voltage.
 2. An apparatus as claimed in claim 1,wherein the additive voltage is additive irrespective of polarity.
 3. Anapparatus as claimed in claim 1, wherein the voltage means is responsiveto a trigger means.
 4. An apparatus as claimed in claim 3, wherein thetrigger means enables the voltage means at a predetermined line voltage.5. An apparatus as claimed in claim 1, wherein the voltage meanscomprises a step-up transformer.
 6. An apparatus as claimed in claim 1,wherein the voltage means serves to amplify a trigger signal, theamplified trigger signal being applied across the main electrodes of thespark gap to fire the spark gap.
 7. An apparatus as claimed in claim 1,wherein the voltage means is provided in series with the spark gap. 8.An apparatus as claimed in claim 5, wherein the transformer has atoroidal winding.
 9. An apparatus as claimed in claim 1, wherein thespark gap is a lightning arrestor.
 10. A method of igniting a spark gap,the method comprising the steps of:monitoring a voltage across a pair ofline voltage rails for an overvoltage condition, at an overvoltagecondition, providing an additive voltage in electrical series with thevoltage across the main electrodes of the spark gap to provide a totalvoltage across the main electrodes of the spark gap which exceeds thevoltage across the pair of line voltage rails at such time.
 11. A methodas claimed in claim 10, wherein the voltage at which an overvoltagecondition is determined is less than a spark gap ignition voltage. 12.An apparatus as claimed in claim 2, wherein the voltage means isresponsive to a trigger means.
 13. A system adapted to initiate a firingof a spark gap in response to a transient or overvoltage condition inrelation to a line voltage across a pair of voltage rails, the systemcomprising:an arrestor including the spark gap coupled between the linevoltage rails, the spark gap comprising a pair of main electrodesbetween which a main discharge current will flow between the linevoltage rails as a result of the firing of the spark gap, and voltagemeans, operatively coupled to the spark gap, for selectively providing afiring voltage exceeding the line voltage across the pair of mainelectrodes upon an occurrence of a predefined overvoltage condition. 14.A system as claimed in claim 13, wherein the voltage means isoperatively coupled in series with the spark gap between the linevoltage rails.
 15. A system adapted to initiate a firing of a spark gapin response to a transient or overvoltage condition in relation to aline voltage across a pair of voltage rails, the system comprising:anarrestor including the spark gap coupled between the line voltage rails,voltage means, operatively coupled to the spark gap, for selectivelyproviding a firing voltage exceeding the line voltage across the sparkgap upon an occurrence of a predefined overvoltage condition, whereinthe voltage means comprises a step-up transformer having a secondarywinding connected in series with the spark gap.
 16. A system as claimedin claim 15, wherein the transformer includes a primary windingenergized in part by an overvoltage condition trigger element.
 17. Asystem as claimed in claim 15, wherein the transformer has a toroidalwinding.
 18. A system as claimed in claim 17, wherein the secondarywinding produces a relatively low inductance.
 19. A system as claimed inclaim 18, wherein the inductance does not exceed five microhenrys.
 20. Amethod of igniting a spark gap operatively coupled between a pair ofline voltage rails, the spark gap comprising a pair of main electrodesbetween which a main discharge current will flow between the linevoltage rails as a result of the igniting of the spark gap, the methodcomprising the steps of:detecting an occurrence of a voltage across theline voltage rails reaching a predefined overvoltage level; and upondetecting the occurrence, providing a firing voltage across the pair ofmain electrodes whereby the firing voltage exceeds the voltage acrossthe line voltage rails at such time.
 21. A method as claimed in claim20, wherein the providing step includes a step of providing an additivevoltage in series with the voltage otherwise present across the sparkgap.
 22. A system as claimed in claim 15, wherein the secondary windingproduces a relatively low inductance.
 23. A system as claimed in claim22, wherein the inductance does not exceed five microhenrys.